https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87106
--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Arthur O'Dwyer from comment #4) > Have you seen my libc++ patch on the same topic as yours? > > https://quuxplusone.github.io/blog/2018/07/18/announcing-trivially- > relocatable/ > https://github.com/Quuxplusone/libcxx/tree/trivially-relocatable/include I am not sure I should look too closely for copyright reasons. Maybe I can... I did read the papers though. > Specifically, the piece that I think is still missing from libstdc++'s > implementation (besides all the cool stuff that you'd get from the > attribute) is the trait `__has_trivial_construct<A, T, T&&>`. I already filed Bug 87604 for that. > This trait > allows you to write your `__relocate_a_1` generically, instead of > special-casing it for `std::allocator<T>` in particular. (So for example it > could also get picked up for `std::pmr::polymorphic_allocator<T>`... I am not particularly interested in polymorphic_allocator. The patch is still missing more important pieces, like the ability to actually specialize __is_trivially_relocatable (I already have another patch locally with the missing piece). > I hope we get P1144 so that you don't have to waste time and brain cells > specializing `__is_trivially_relocatable<T>` for std::string and std::pair > and so on. std::string is not trivially relocatable in libstdc++, so I won't waste any time there. IIRC, one difference with what you did is that I use relocation even for some types that are not trivially relocatable (in particular std::string), because it actually helps, as shown in the first message of this bug report. > Complete tangent: I'm confused how vector.tcc is allowed to use "if > constexpr" in C++11 mode. > https://github.com/gcc-mirror/gcc/commit/e9f84d4c#diff- > 05b068171cedf9d0176bada75d7dd112R76 It is enabled as an extension and produces a warning which is disabled in system headers.
